Further musings on Enfield crankcase breathing *updated*

[stinkwheel]

Long, boring and probably pointless posting. More for me getting my thought processes in order.

The breather arrangement on my bike is a lash-up and ongoing headache.

It's a pre-unit bike with a dry sump and an integrated (but effectively seperate by design) oil tank.

What it should have by design is a duckbill breather coming from the crankcase to atmosphere. Negative pressure is maintained. Blowpast is vented. Planets align, zen occurrs.

What I got, due to it being a very late model was no breather at all in the crankcase itself. A hole drilled in the casting between the crankcase and the oil tank. A duckbill breather running from a hose-tail on the oil tank to a catch-can. A one-way hose running from the catch can to a stub on the timing chest supposedly to return any liquid breathed out.

What this gets you is a wheezy engine prone to mayonaise in the oil and slightly positive crankcase pressure.

Catch can contents after 600 miles.
https://i48.photobucket.com/albums/f216/stinkwheel/distributor/DSCN0705.png

First attempt at fixing this was to ditch the catch-can, vent the oiltank breather to atmosphere with a simple duckbill and block off the return stub. That got the mayonaise beat. Breathing still seemed erratic at best. Oil consumption was (and still remains) horriffic.

Having trashed a head through the shear quantity of oil being burned I attempted to re-create the original breather system. This meant drilling a hole into the crankcase, fitting a stub and attaching it to a one-way valve. Venting any positive pressure to atmosphere. I used a diesel engine one-way mechainical valve this time.

Broadly sucessful. This vents a huge amout of gas/vapour compared to the previous breather. I'd say 5 times as much. I can be fairly confident this is creating a slight vacuum. I am however still consuming an inordinate amount of oil.

Breather pipe. Vertical copper pipe is an attempt to reduce oil loss by misting (most of it should run back down the pipe)
https://i48.photobucket.com/albums/f216/stinkwheel/distributor/CIMG1318_zps7827d360.jpg

Now to the question. I was having a play with the bike today. In particular, seeing what I ought to be doing with the two stubs (leading into both the timing chest and the oil tank). I had previously blanked off the timing chest stub and left the duckbill hose on the oil tank one in case the new breather became blocked.

So using my exhaust balancer gauge I can see a very slight vacuum on the end of the timing chest stub. I'll call that a win and leave it blanked off.

The oil tank breather stub however... It kind of blows gas gently to-and-fro at tickover, consistant with the piston going up and down too slowly to activate the one-way valve in the main breather.

With revs though, there is a surprisingly powerful vacuum. enough to hold the end of an 8mm hose onto a wet fingertip. True to form, if I block off the end of the new crankcase breather, it reverts to being pressurised and venting the crankcase pressure through here.

So I'm not sure exactly what to do with it. In an ideal world, I'd go in and block up that hole between the crankcase and the oil tank that wasn't in the original design. Trouble is, that would mean taking the ENTIRE engine apart.

I'm pretty sure I don't want a vacuum in my oil tank so blanking that stub off probably isn't a great idea?? I'd imagine it's not helping the feed pump among other things.

But if I leave it to vent naturally, it's going to be drawing air in through the oil tank breather stub and from there ventilating into the crankcase (hopefully not taking oil with it). Essentially creating a through-draught and reducing the level of vacuum in the crankcase.

But can you have too much crankcase vacuum? Is there even a number on it? (I could probably measure it with a manometer). Would simply avoiding positive pressure be sufficient?

TL;DR

It's an old fashioned engine that's been fucked with to pass emissions. I've fucked with it further to try to undo the damage.

I have a choice of leaving a vacuum in my oil tank or allowing it to ventilate to atmosphere. Doing the latter will radically reduce the vacuum in the crankcase. Is there a minimum qualtity of crankcase vacuum?
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[stevo as b4]

I can't see why you'd want any vacuum in the crankcase, as wouldn't that increase pumping loses and make it more likely for the piston to try and draw oil mist up the bore or past the rings?

How do the modern Enfield engines have their breathing system plumbed in?

On my car engine I have a breather running into a catch can, with a filter on the top, and also a 22mm hose tapped into the block, that runs from the bottom of the catch tank and should act as a drain hose. In that hose is a steel mesh filter to try and stop oil mist rising into the catch tank, as well. I don't get much oil on the breather filter or under the bonnet, so it seems to work I guess.

[Triton Thrasher]

[Triton Thrasher]

What are you using as a one way valve?

Reed valves for 1970s BMWs work well, as do some that a German firm sells for Yamaha XS650s. The old Enfield duckbill worked ok too. Why not just copy the older Bullet exactly?

The reed valve should be close to the crankcase. I don't understand your description of the plumbing into the oil tank and all that. Block the hole that goes from crankcase through into oil tank.
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[stinkwheel]

[spottedtango]

Another problem with leaving a through draft in the oil chamber is its drawing air from outside which can be full of moisture and turn your oil faster.

Having a neutral crankcase pressure it won't draw any blowby out meaning that again the combustion gases mixing with the oil will turn the oil faster making it get more acidic. Also putting pressure on your engines seals

To try and answer your question you can have too much when the piston is on the upstroke, the vacuum in the case will sap power from the pistons upward movement. Too little vacuum or positive crankcase scenario and the case will become pressurised on the down stroke sapping some power on the pistons downward movement and as said before pressuring your seals. As for putting an exact value on what minimum vacuum negative vacuum should be I'm not sure however I did find a site explaining more of the details behind crankcase pressure more precisely the crankcase aspiration pressures for a single cylinder. Hope this helps.


https://nortonownersclub.org/support/technical-support-commando/crankcase-breathing

[Triton Thrasher]

Consider that your oil burning may not be caused by the breather.

Anyway.....
A spring and ball diesel fuel valve like that will not open and shut fast enough and that one is rather distant from the crankcase.

BMW reed valve, about an inch diameter so needs something made to hold it.

https://bmwmotorcycletech.info/breather_valve.jpg

Scooter EGR valve, popular with the XS650 and Norton Commando crowd.

https://images.xs650shop.de/15_0677

Ok- isolating the tank from the crankcase is out, at least for now.
With an actual working reed type non-return valve, you may still manage to get some depression in the crankcase.

Thinking about it, the oil tank shouldn't need a breather of its own, if its air space connects to the crankcase and that has a breather.

You will never generate enough vacuum in the crankcase to do any harm, whatever people think that harm might be. Oil will still run down to the pump, because it is sitting in the same vacuum as the tank.

Smoke from the breather when the engine is cold doesn't matter if it stops when the engine warms up.
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[jimspeed]

Surely if the breathers are venting to atmosphere then you want them tee'd together then a valve and decent length of pipe ?
I'd be more worried about a vacuum on one pipe pulling in dirty dusty air into the crankcase
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Hyosung cruise 125(passed test on, sold) Kawasaki el 252 (better than expected but sold on) Kawasaki GPZ500S first "big"bike.(sold) ZZR600 E5..Z750 2007,ER5, currently on a 2008 Enfield bullet electra x and loving it..
,"Alpha-9: Is there any correlation between dyno rod and dyno kits?"

[mysterious_rider]

From what i know...
The crank needs to breath. There will be positive pressure in there (gases getting past rings) so i wouldnt fit a one way valve. Because it pulses too
That pipe you have built looks very skinny for the pulses that engines going to emit. Personally id lop it off and fit fatter tubing over the elbow joint and run it up and into nothing. Then cable tie it. Or like cars and fit it inside the airbox.

It wont be the cause your oil burning.

Oil burning could be leaky valves or rings. Probably caused by running the bike in like a pussy. Well its just a thought.

How much oil loss are we talking? And how many miles she on? I considered one of these bikes but they are too small for me sadly.
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KAWASAKIIIII

[Triton Thrasher]

[jimspeed]

[Triton Thrasher]

[spottedtango]

Also when it comes to multi cylinder engines you'd think the crankcase pressure would remain fairly neutral (e.g in a 4cyl 2 pistons up 2 down) but because of the blowby the case becomes positively charged and that's why there's a need for a negative vacuum to vent the blowby to the atmosphere.

[Triton Thrasher]

A multi cylinder engine could be the answer.
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[Kickstart]

[Robby]

The way to balance this out on a modern (post-1970) Japanese engine is to vent the crankcase breather into the airbox, with a catch can or baffle plate in the middle to condense oil vapours, and no cocking around with one-way valves.

Can you try a similar thing? Ditch the valve, replace it with a catch can, and plumb the vent line into the back of your air filter. That should give you a balanced system pressure-wise. I would also consider a simple atmospheric vent (a small drilled hole) on the oil tank, probably on the filler cap.

Your current setup with the one-way valve must be giving a fairly high vacuum inside the crankcases when the piston is rising. I'm not sure how that is a bad thing, but it seems wrong. Balance is good, big pressure fluctuations are bad. The valve is forcing the pressure to fluctuate.

[stinkwheel]

Something is causing the oil loss. It'll go through maybe 300ml every 150 miles. Always has from the day I got it with 300 miles on the clock. Now has closer to 60k. It's a pretty rediculous amount of oil to burn/lose.

Things I know it isn't include:

Leaks. Floor is clean.

Wet sumping. Never more than 30ml of oil if I undo the sump drain plug

Blowpast . I replaced the original piston thinking this was the problem. I then replaced the barrel and piston some time later when I cracked the original barrel while removing the head for a de-coke.

The newest one is a British made alloy barrel with a higher compression piston and wasn't really run in at all. I just rode it as normal for 200 miles then changed the oil and filter. I then rode it from Amsterdam to Leipzig in a day.

Over pressure. Scavenge pump pressure relief valve fitted. I have high flow oil pumps fitted but it burned just as much poil before I fitted them.

Excessive breathing. It breathes a lot, but not as much as it's using. It's mostly yakky emulsion-type vapour that comes out. Around 50ml every 150 miles if you put a bottle over the end of the breather. Just enough to mark its territory when parked.

I keep coming back to oil stems. However, I replaced the valve guides for longer ones. Then after the original head dropped it's valve seat, I fitted a tuned head from Hitchocks performance which has been fettled by men in brown coats. I've since fitted valve stem oil seals (off an old mini of all things).

None of the above made any difference. Junking the catch-can stopped the mayonaise problem that was slowly killing it.

It doesn't smoke much. Certainly not once it's warm. It apparently gives out a little puff of smoke on the overrun. It also smokes pretty badly if you park it on the sidestand with the engine running (to the point it'll oil-up and conk out). I have no idea why.

It seems a bit pointless venting the oil tank by drilling a hole when it has a hose-tail fitted. It's currently tucked up inside the battery box so it doesn't suck in too many nasties. I may stick a small K&N over the end of the hose if it seems better.

For interest, I just went and found a picture of what functioned adequately as a breather for the first 65 years of the production run on these bikes which is what I've tried to replicate. It's just a stub into the crankcase with a rubber duckbill on the end.
https://i48.photobucket.com/albums/f216/stinkwheel/standardbreather.jpg

Triton: That EGR valve looks interesting. I've also heard of people using turbo check valves. My concern is how much liquid will it cope with?
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Triton Thrasher]

I suppose you are already using good thick 20W/50 oil.

How does a scavenge relief valve work? On first thoughts it sounds like a bad idea. You want all the oil in the cases to be sent back to the tank, pronto.

So you're another one with a valve seat falling out!
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[stinkwheel]

[smegballs]

[stinkwheel]

[mysterious_rider]

Hm. Change brand of oil. It shouldnt get that mucky . maybe thats its loss. Emulsifying and chucking it out of the breather. Better that stuff stays out though..

Different oil and report back?

I still think its burning some too . can you see/smell it?
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KAWASAKIIIII

[stinkwheel]

It gets whatever oil is cheap now given how much it uses.

I generally use a high detergent diesel oil but I've tried it with all sorts.

I even wondered if I was overfilling it, so I pumped it out to completely empty and filled with the specified oil volume which took it to the middle of the dipstick.

I'm also pretty sure it's burning the oil. The question is WHY? The fact is, nothing I've done has made much difference to the oil consumption and there are no top-end engine componants that haven't been replaced with higher quality ones.

I'm even wondering if I should get (another) new piston and have it bored a bit tighter than spec.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Triton Thrasher]

What spec is it bored to now?

Alloy barrels call for a smaller piston clearance than cast iron.
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[stinkwheel]